The present invention relates to cams of the flat curve type, that is, cams in the form of grooves in the surface of a flat plate. Such cams form one type of the general class of box cams, wherein the cam follower is positively constrained to move in both directions, that is, inwardly toward the center of rotation of the cam as well as outwardly away from the center of rotation. This is in distinction to the more common type of cam, such as a plate cam, where the cam shape is on the periphery of a rotating plate and the cam follower is constrained positively only when engaged with the rise portion of the cam periphery, the inward movement of the follower toward the center of rotation of the cam, when in contact with a fall portion of the cam, being caused by a spring or the like.
Box cams, constraining movement of the follower in both directions, are particularly suitable for high precision mechanical instruments, such for example as motion picture cameras and motion picture projectors, where rapid movements with high rates of acceleration and deceleration may be required, and where it may be desirable to dispense with the springs that would be required if peripherally shaped plate cams were used. Because of limited space available in precision mechanisms such as motion picture cameras and projectors, it may be desirable to combine two or more cams as separate grooves on a single flat cam plate. If the necessary shape of the cams is such that the cam grooves or curves intersect each other, this creates problems to insure that the respective cam followers do not accidentally enter the wrong cam groove at the points where they intersect.
The ideal cam follower for use with a cam in the form of a curve or groove in a flat plate, is a cylindrical pin or roller fitting snugly in the width of the groove. However, this cannot be used as the follower in the conventional form of cam groove construction where two grooves intersect each other, because of the danger that the follower may enter the wrong groove at the point where two grooves intersect. Therefore, to prevent this, it has been proposed to use a sliding block rather than a cylindrical pin or roller, the block being so shaped that it cannot enter the wrong groove at the intersection. This creates difficulties, however, if the shape of the cam curve has portions of very small radius.
This problem is solved, according to the present invention, by using a novel combination of width and depth dimensions for the cross sections of the respective cam grooves. The cam followers fit snugly in the width of the grooves. Therefore, the cam follower of a wider groove cannot pass accidentally into a narrower groove where the two grooves intersect. Also, the narrower groove is made deeper than the wider groove, and the cam follower of the narrower groove extends deeper into this groove than the depth of the wider groove, so cannot pass accidentally into the wider groove at the point of intersection.
In a modification, as described below, the main or force-transmitting parts of the respective cam grooves may all be of the same width, but narrower guiding grooves of different widths and depths may be formed in the bottoms of the main force-transmitting grooves, to receive guide pins which prevent entry of the followers into the wrong grooves but which do not come under stress except momentarily at the points of intersection.